At the Connections Museum in Seattle, we proudly exhibit a Panel switch from 1923. We have it connected to a Linux system through a T1 line via a Western Electric “D4” channel bank. Since support for the “revertive pulse” signaling that it uses had never been needed in the outside world, we had to write our own modifications to the analog telephony kernel drivers to make it run.

We now have working support in both directions - sending the signaling pulses as well as receiving them. We believe that makes it the oldest working hardware with support running in the Linux kernel.

I’ll go over:

• the basics of the Panel switch itself, how it communicates with other analog switches, and how that turns into a digital trunk
• the architecture of Asterisk — what logic is in the kernel and why
• the painstaking process of adding this support to a kernel driver
• and how we use all this today to interface this century-old machine to the internet.